With the advent and use of non-mechanical inputs (e.g., virtual keys, touch screens, RFID with magic touch (i.e., near field communication)—see “Now Nokia has a ‘world first’ magic touch,” Silicon.com, Nov. 4, 2004), it is often desirable to provide a form of active feedback for a user. For example, in response to a user touching a “button” or region on a touch screen, a vibration can act as tactile feedback or a sound can act as audible feedback. Vibration is also often used to provide a silent or less audible alert for a user.
One prior art solution is to use a vibrating alert that provides a separate vibration as feedback. However, due to software and hardware variations, it can be difficult to accurately synchronize the timing of the vibration or sound. Furthermore, the vibrating alert should be strong enough that a user can feel or hear it. Even so, fast, sharp feedback pulses with an alert-capable actuator are generally difficult to construct.
Another prior art solution currently seen as promising comprises piezoelectric (PE) actuators. The PE actuators can provide sharp feedback imitating key presses. However, PE actuators are costly (e.g., due to a special driving stage), may not be durable and may have issues with regard to the required mechanical tolerance and durability of components. Furthermore, PE actuators may have a disturbing sound output from the sharp vibration (i.e., the vibration can cause an annoying sound). This last issue can be addressed but requires further optimization of components (e.g., the driving electronics).
Multi-function devices (e.g., a loudspeaker further acting as a vibration-producing unit) can be used to provide both sound and vibration outputs. A disadvantage of such devices lies in the reduced sound quality. In addition, the strong mechanical resonance of the moving magnet can be felt as “rattling” when handling the device (e.g., a non-rigid, “ringing” feel, or a perceived mechanical quality issue). Furthermore, sharp pulses typically cannot be produced (e.g., around 150-200 Hz.).
Some current flat panel speaker systems also provide tactile feedback on the radiating surface. However, these systems often carry specific constraints, such as a requirement for increased durability due to the harsh handling a mobile device may receive.